First of all, I haven't been on the forum in a long time. so about a year ago I started my own little thing called the Omega Project. This was just a challenge to build a semi-automatic if not automatic combustion spudgun. Of course all of my ideas dead-ended with finding a way to vent CO2. Then I gave up on it. I searched the internet and never found anyone who has tried; I'm sure people have. The concept I came up with was some kind of air piston that could push out exhaust and push in fresh air. This was about 10 months ago and it looked really good on paper but I never got around to testing it. Then a couple of days ago I found a discussion about that Tippmann paintball gun that uses propane so I found the design diagrams for it and learned how it worked. It uses the air piston concept and it works. So that same day I went out and bought a little basketball pump and installed it on my little 2" X 9" mini spudgun. This little spudgun never got much attention after I built it because the "fan" is mounted in the cap and you have to take the cap off to vent it, using lung power. therfore, I could only get off a shot every 45 seconds. Now I can get a shot off every 8 seconds because all you have to do is pump three times to vent, inject the propane, load, and shoot. I feel like I may be a step closer to a semi-automatic combustion. I will post a picture of this cannon later. I also want to open up my project to everyone else and I hope someone will make something even better. I look forward to hearing suggestions.

i say take a shotgun, if you have one, or barrow one from someone, then take it apart and see how the loading mech works, then replicate it and us pre-fueled shells. i think that would be pretty cool. of course it would be a big project and would require more than just tinkering to get it to work, but it would be worth it in my opinion.

one thing that would make it much much easier to build is simply have it be single shot and you can speed load it, like how officers are trained to speed load when they are out of ammo.

if you dont know how to speed load, basically what happens is when the last shell if fired, you rack the bolt back, then drop a shell into the ejection port, then rack it forward. look at this video for a demonstration.

I like that guy's firestorm design, but it has many flaws and I don't think it would work as shown. I did notice that he used the air piston concept to vent so now i realize how many other people have thought it up. I also like the 3 way solenoid(or how ever you spell it) that the guy on advanced spuds used for a meter. Thanks for the links.

You've already seen it but my carbureted bolt action is "pump" action. It is similar to the Tippmann C3 painball gun. The reason why it can't be automatic is because the energy from combustion is used to propel the round, not reset the chamber. To do that, you need a larger chamber to have leftover energy to reset the chamber. I've done a lot of thinking based on the design your trying to accomplish. The closest I've gotten to semi-auto is the Carbureted Bolt Action Combustion. All other designs I've tried always end up looking like an internal combustion engine with the exhaust as the barrel and the crankshaft loading the ammo.

EDIT: You me and spudfarm should run off this idea. We all have a common goal. Maybe I can try to rework my carbureted bolt action and we can run with it. The auto combustion can't possibly be only limited to the internal combustion engine.

I like that idea, it sure would speed up the process. I would like to have at least a semi-auto design built and operating before I go to college in August. Of course college may help me even more since I will be pursuing a major in engineering.

How about when you pump the action, the grip moves forward onto the exhaust valve of an auto-refilling fuel meter and straight into the chamber. On the same stroke of the grip going forward to fuel the chamber, you could have either a gravity-fed magazine or a spring loaded magazine fit in behind the grip and have (for example) golf balls popping into the barrel via a hole which is usually blocked by the grip and will only allow ammo to pass through it when the grip is pushed forward to line up the holes.

Yes it would seem like using pressurized fuel would be ideal. The only way, that I've found so far, to have a carbureted semi would require either a coaxial combustion or divert the bolt around the chamber. Both are possible but not very efficient. I'm currently looking for a way around this reality but I haven't found anything yet. If possible however, a carbureted semi would be much lighter than a pressurized fuel based system. There wouldn't be any tanks or valving on the exterior of the gun. This makes the gun possible to model after a real one or be more ergonomic and practical. If we go for the pressurized system there is no way to disquise it as a real gun unless the tanks are small or strangely shaped. Binder17, it's your decision.

I am not too enthusiastic about a pressurized system. It seems too complex and too much to deal with. So we should look into the carbureted system for now and also think of other ways. I am going to get markfh11q in this too since he lives nearby my house.

I have my air pump ventilation system installed on my small cannon. It works well in ventilating the chamber but not as well as I would like it to. The design is promising though, they got it to work on that propane paintball gun.

All that would need to be done is a cannister of propane at the end of the grip, when the grip is pumped forward, it hits the top of the propane cannister and squirts a small dose of propane into the chamber. Simple as..